resource: Don't log error of oc_mutex_free

resource: Don't log error of oc_mutex_free

IOT-2177 Don't log error if oc_mutex_free is called with null.

Change-Id: I1e589304f9bce866f5ba18800292204c78d43590
Signed-off-by: Way Vadhanasin <wayvad@microsoft.com>
Reviewed-on: https://gerrit.iotivity.org/gerrit/19433
Reviewed-by: Dave Thaler <dthaler@microsoft.com>
Tested-by: jenkins-iotivity <jenkins@iotivity.org>
Reviewed-by: Dan Mihai <Daniel.Mihai@microsoft.com>
(cherry picked from commit 36525788ca27c32354accc504f6dcc5875e1c902)
Reviewed-on: https://gerrit.iotivity.org/gerrit/21141